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Old 03-10-2013
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Re: Battery life short? What to check?

After you get done answering MaineSail's good questions, you will want to look at the whole system as a whole. Electrical systems are a whole entity on a boat as important as an engine and can't be piece mealed . Also it is an expensive system you can waste and save money in with good planning They are only as good as their weakest point.

So you have batteries, charging methods, amp hour load, monitoring to simplify it.

Ah load- what is your normal daily use. Calculate using refrig, pumps, electronics, lights, windlass, etc. This will allow you to determine whether you have enough or what you need in battery amp hour (ah) power. And how do you se your boat.? Weekends , wee is, days,

Charging methods. Do you have a modern 3 stage charger? Are you at a slip long enough to maintain 100 % charge, Do you have solar to maintain 100% charge while underway? What type of alternator? Do you desulfate you batteries if wet.

Batteries- you have two types t o charge gel and AGM, usually a no no. What batteries best suit your use, wet, AGM, gel. Are group 31 the best ones for you. In most instances I like 6 volts as their plates are heavier and you get as much as 3 but always twice as many deep cycles and usage out of a battery. Also if you can fit their height, 2 -6 volt will give you twice the ah as one group 31 in almost he same footprint. You could literally double you ah in you space by going to them and also double your number of deep cycles thus doubling you lifetime.

In this part read up on battery charging, 50% discharge. Charging back to 80-85%, time it takes to get back to 100%. Amount of usable ah. In a group 31 bank for instance each battery may be 110 ah. You can only discharge or have useable 50%. So you may have 220/2= 110 ah usable. If your daily ah diet is let's say 70-80 ( you have refrigeration) that's 1.5 days. If you don't have solar or the dock to recharge your engine may bring back o 85% or 187 ah the next day you se 70 ah you are own at he adage again 187-70=117 and this continues till you get back to the slip and can get back to 100%. In the 6 volt scenario you have 4 of them of 440 ah at 12 volts ( wet ones can be had for less than $100 a piece). So with 440 ah you have 220 available. You say out overnight and you use 70 so your down to 150 available ( 2 more nights without charging) and are at 370 ah which is almost the 85% you can get o without the solar or battery charger. You motor for a few hours. Battery acceptance is much lower past 85% so maybe you can only put in 20 ah so your back to 390. You stay out another night without the dock and use 70 more. Now yor down to 320 ah but 100 usable still in reserve. You motor two hours. With an average 50 amp alternator you re back to 370 ( 85%) in one hour. Then lower acceptance again. And so on. Maine sail will correct my figures, but you get the scenario. If you do weekends as most t least do having 440 ah capacity is never having to worry.

Also you must take care of the batteries. Desulfating if necessary. Temp control etc. most batteries should last 5-7 years easily if maintained. Otherwise gets expensive. AGM / gel are specialized batteries and have their place, but only if he whole system is up to snuff to keep them charged as they are only out effective if kept near 100%.

Monitor. That's how you keep track of the above. It's simple and cheap with the orrect monitor and you need to look at it a few times in a day quickly for 20 seconds o make ure its ok.

Do some reading and listen to Maine you will avoid lost of extra expense and aggrevation You won't worry bout power or adding something new to your boat.
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